Ketogenic Diet and Thyroid Function: A Delicate Metabolic Balancing Act

The ketogenic diet (KD), a high-fat, low-carbohydrate diet, causes profound metabolic adaptations that go beyond energy production and affect endocrine function and thyroid hormone regulation. By shifting the body’s primary fuel source from glucose to fatty acids and ketones, the KD alters insulin signaling, inflammation levels and deiodinase activity, which together affect thyroid hormone metabolism. While this metabolic shift offers potential benefits such as improved insulin sensitivity and reduced systemic inflammation, it also raises concerns about reduced triiodothyronine (T3) levels and altered hypothalamic–pituitary–thyroid (HPT) axis dynamics. This review explores the mechanisms by which the KD affects thyroid function, highlighting both the potential therapeutic benefits and associated risks. Special attention is given to how genetic predispositions, gut microbiota composition and sex-based hormonal differences influence thyroid adaptation to a KD. In addition, there are indications that the influence of the KD on cell metabolism could have therapeutic potential in conditions such as autoimmune thyroid diseases and thyroid cancer. Understanding the delicate balance between the benefits and risks of KD for thyroid health is essential for optimizing its clinical applications and defining individual nutritional strategies.